1. Field of the Invention
This invention relates to the art of transforming rough diamonds into faceted, brillianteered diamonds, and, more particularly, relates to a method for cutting and faceting diamonds in such a way that the yield obtained in the finished product is significantly increased over yields previously obtained by existing cutting and faceting techniques.
2. Description of the Prior Art
The art of polishing facets on gemstones (other than diamonds) has been around for many centuries. The first known attempt to facet a diamond is believed to have taken place in the eleventh century. At that time, eight triangular faces were polished in the rough diamond, creating what became known as the xe2x80x9cpoint cutxe2x80x9d, which resembled a pair of pyramids joined at their bases.
In the early part of the fourteenth century, a single, horizontal planar facet was introduced, which became known as the xe2x80x9ctablexe2x80x9d, leaving four natural beveled surfaces that created the crown. Further refinement of this elemental configuration has resulted in, among others, the round brilliant cut, which is the most popular faceting configuration for today""s diamonds.
Currently, diamonds are first cut into a top or crown and a bottom, base or pavilion, and a girdle lying between the two in a horizontal plane. Anywhere from four to sixteen sections (top primary facets) are cut into the top section, oriented at roughly 34.5xc2x0 above horizontal. Anywhere from four to sixteen sections (bottom primary facets) are also cut into the bottom, oriented at roughly 40.75xc2x0 below horizontal. This phase of the cutting process is known as xe2x80x9cblockingxe2x80x9d. It is almost universally accepted that these proportions and angles for brilliant cut diamonds are necessary to produce maximum brilliancy with a high degree of dispersion or xe2x80x9cfirexe2x80x9d. Thereafter, additional facets are added to the top and bottom sections in a second phase known as brillianteering. This approach is shown in FIGS. 1 and 2. FIG. 1 shows a stone with eight main facets in the crown and eight main facets in the pavilion (i.e. after the rough has been xe2x80x9cblockedxe2x80x9d), while FIG. 2 shows the same stone after brillianteering facets have been added.
Eventually, stone cutters became aware of and began to understand the effects of refraction and reflection on the optical path of light within the gem and how to control it through angles, surfaces and proportions. As the art of gem cutting evolved, it has become widely accepted that the brilliant cut is the optimal cut for simultaneously maximizing the fire, lustre, scintillation and brilliance of the stone. Since, in general, the stone is viewed by looking down at the table and crown facets, it is desirable to induce the maximum amount of light possible through the table and crown facets, down into the stone where it is reflected off of the interior surfaces of the base facets across to the opposite base facets and then back out through the table and crown facets to the viewer. The more optimal the configuration of the stone, the more even, intense and uniform is the thus reflected dome of light perceived by the viewer.
Diamonds have various characteristics that distinguish them from other gemstones. One characteristic is brilliance, which can be further categorized into external and internal. External brilliance, also referred to as lustre, generally refers to the amount of light that impinges on the top of the stone and reflects back, rather than light that enters the stone. Internal brilliance is determined by the light rays that enter the crown and reflect off the base facets and back out through the top or crown as amplified (i.e. focused) light.
Another characteristic of a diamond is dispersion, also known as fire, which is a measure of how much the white light is broken up into the spectral colors. A ray of white light striking a prism will be split up into component colors of red, orange, yellow, green, blue, indigo and violet. Dispersion is maximized when a ray of light is reflected totally from base facets and strikes the ground facets at the greatest possible angle. Dispersion is observed when a diamond moves relative to an observer.
Another characteristic of a diamond is scintillation, which is an indication of the different light patterns obtained when the stone is moved under light. Expressed in another way, scintillation is the quantity of flashes observed from the diamond when either the diamond, light source or observer moves.
The refraction index for a diamond is 2.417, which is the highest for a transparent natural gem. The amount of dispersion of light, or fire, depends on the original angle of incidence and the distance the light travels inside the stone. The larger the angle of incidence, the larger the amount of refraction within the stone, and the greater the dispersion. White light is a blend of the spectral colors and because each color slows and bends differently this causes the light to disperse into spectral colors, which creates the fire within the diamond.
Today""s diamond consumer is typically a highly discriminating and well educated shopper, looking for the highest value out of his or her investment. At the same time, the diamond supplier wants to obtain the highest yield from a given piece of rough. Currently, 10%-50% retention is good for a brilliant cut diamond. Since the price per carat increases exponentially in proportion to the carat weight of a particular stone, it is highly desirable to increase the yield, and conversely decrease the waste, from a given rough. The same light and dispersion can be obtained at less cost through weight retention during the faceting process.
In the past, however, the yield obtained in creating a faceted stone has been unnecessarily limited due to the belief that, in order to obtain acceptable light dispersion (i.e. reflection and refraction), the angle of the base facets should not exceed 43%.
Thus, the desire for weight retention has given way to what has been believed to be the need to keep the angle of the base or pavilion facets in a range of between 38xc2x0 and 43xc2x0 relative to a horizontal plane. The result of this practice is that, in order to cut the base facets at the presently specified range of angles between 36xc2x0 and 43xc2x0, an unnecessary amount of waste occurs during cutting of the stone, including unnecessarily limiting the diameter of the finished product.
Therefore, it is desirable to present a method for creating a higher yield diamond which exhibits virtually identical visual effects and light performance as today""s modern or brilliant cut.
One attempt at increasing the weight of diamonds utilized a greater table spread (the ratio of the table diameter to the girdle diameter). However, it was found that the circumferential surface of the girdle would be reflected off of the base facets through the table, creating what is know as the xe2x80x9cfish-eyexe2x80x9d effect. Attempting to decrease the base facet angle to prevent this unwanted effect deleteriously affected the stone""s fire.
U.S. Pat. No. 5,970,744 to Greeff and assigned to Tiffany and Company is directed to a cut cornered mixed-cut square gemstone having a two-step crown, a girdle, and a pavilion. The pavilion sides and corners are defined by eight rib lines which extend continuously from the girdle to the culet. The first crown step has an angle of about 41xc2x0-44xc2x0 relative to the girdle plane and the angle of the second crown step is about 36xc2x0 to 39xc2x0 to the girdle plane. The rib lines in the pavilion are preferably at an angle of between 38xc2x0-42xc2x0 relative to the girdle plane.
U.S. Pat. No. 5,657,646 to Rosenberg discloses a new cut for a precious or semi-precious jewel having two or more culets and at least one additional facet extending from the end of the jewel (girdle) to the extra culet at an angle of 41xc2x0 (for diamonds).
U.S. Pat. No. 5,072,549 to Johnston discloses a method of cutting facets on a gemstone, as well as the resulting stone, wherein facets are cut which produce a five-legged star which appears beneath the gem table. The product produced by this method comprises a pavilion having thirty facets and fifty edges, a crown having twenty-one facets and thirty-five facets, and a five-sided girdle.
U.S. Pat. Nos. 3,286,486 and 3,585,764 to Huisman et al disclose a brilliant-cut diamond having a pavilion formed of seventy-two facets and a total of one hundred and six overall. In the pavilion, there are eight kite-shaped (main pavilion) facets at 41xc2x0 relative to the horizontal girdle plane, sixteen kite-shaped facets at 45xc2x0-47xc2x0 relative to the girdle plane, sixteen star or diamond shaped facets at 53xc2x0 to 54xc2x0 from the girdle plane and 32 triangular facets at 58xc2x0-60xc2x0 relative to the girdle plane. As such, the pavilion defines a tapering upper area ranging from 58xc2x0-60xc2x0 to 41xc2x0 at the base thereof. The sixteen kite-shaped facets, although not beginning at the girdle, appear to extend along roughly half of the pavilion. Stones cut in accordance with the Huisman patents are not of higher yield, however, because the star and half of necessity facets are added after the bottom pavilion facets have already been cut.
As a result of the physical principles discussed above, varying the proportions of the facets of the stone will effect the appearance of the stone. At present, the gem industry has accepted the theory that the optimal angle of the base facets is roughly 41xc2x0. It has been stated by one well-known authority on the subject that deviation of 0.25% from that angle will dramatically affect the appearance of the stone. However, the inventors herein have discovered, in the process of attempting to increase the yield for cut stones, that, by blocking the stone in a certain xe2x80x9cmannerxe2x80x9d using the technique of this invention, virtually the same visual characteristics can be obtained while also obtaining upwards of a 15% greater yield than has been available with existing techniques.
As used herein, the term xe2x80x9cdiamondxe2x80x9d refers to both natural and man-made diamonds.
It is, therefore, a principle object of this invention to provide a diamond which exhibits acceptable visual properties while yielding greater weight retention out of a given parcel of rough.
It is also an object of this invention to provide a technique for producing such a diamond.
In accordance with these and other objects, the invention is directed to a method for girdling, blocking and faceting a diamond in such a way that the resulting product has a substantially higher yield than has heretofore been achieved while retaining optimal visual performance.
Another aspect of the invention is the resulting cut stone, which exhibits the aforementioned visual characteristics while being of a higher yield than previously achievable from a given quantity of rough and while maintaining the desirable ratio of diameter to height. In general, the product is comprised of a diamond, which may for example but not by way of limitation be a round brilliant cut gemstone, comprising a girdle, a top or crown above the girdle and a pavilion or base below the girdle. For purposes of this description, the girdle will be deemed to lie in a horizontal plane (xe2x80x9cgirdle planexe2x80x9d). The crown terminates in an upper planar surface known as a xe2x80x9ctablexe2x80x9d, which is generally parallel to the girdle plane. The pavilion ends at its lower most end with a culet, which may be either a point or a planar surface or any other faceting arrangement desired without affecting the scope or principles of this invention. In one embodiment, the pavilion is comprised of a series of facets, some of which make up an upper pavilion, and another series of facets below the upper pavilion facets which constitute the lower pavilion. The stone may be divided into four to sixteen main top facets and four to sixteen main bottom facets as a result of the blocking step, which will be discussed in more detail below. xe2x80x9cBlockingxe2x80x9d is the step in the diamond cutting process in which the initial angles and primary facets are created from the rough stone, and xe2x80x9cbrillianteeringxe2x80x9d is the subsequent step during which secondary or minor facets are polished into the stone.
According to the invention, the height of the upper pavilion girdle is greater than 20% but preferably less than approximately 80% of the total pavilion height. The pavilion height is the distance from the girdle to the culet. The angle of each upper pavilion facet is between 45xc2x0 and approximately 80xc2x0 from a horizontal plane, and the lower pavilion facets are set at the customary angle of 38xc2x0 to 44xc2x0. The crown break angle, which is an angle of the crown facets relative to the girdle plane, is preferably between 26xc2x0 and 35xc2x0.
The resulting visual performance of the stone configured as described herein is surprising and striking, yet virtually indistinguishable from prior art stones, while at the same time resulting in a higher yield for a given quantity of rough material from which the stone is cut.
Such a result is achieved by creating the pavilion break angle, which is the angle at which the upper pavilion facets lie relative to the girdle plane, at between 45xc2x0 and 80xc2x0 during blocking. Additionally, the cutter determines the appropriate position for the girdle to create a larger girdle diameter than has heretofore been achieved, but the average depth can remain similar and even identical in some instances. The xe2x80x9caverage depthxe2x80x9d is the ratio of the height of the diamond to its diameter. Additionally, the lower pavilion facets are cut at the accepted angle of somewhere in the range of 38xc2x0 to 44xc2x0. As stated above, the height of the upper pavilion facets are preferably between 20% and 80% of the overall height of the pavilion. Consequently, the lower pavilion facets are between 80% and 20% of the pavilion height.
It has been found that by blocking the pavilion break angle at an angle of 45xc2x0 to approximately 80xc2x0 and cutting the lower pavilion facets at an angle of between 38xc2x0 and 44xc2x0, a higher yield is achieved than if the pavilion break angle was first cut at 38xc2x0 to 44xc2x0 and thereafter the bottom pavilion facets were cut back further to the 45xc2x0 to 80xc2x0 angle. All that is required, however, is that the upper pavilion facets be cut at the preferred angle range of 45xc2x0 to 80xc2x0 and the lower pavilion facets at the standard angle of 38xc2x0 to 43xc2x0 before any brillianteering facets are made. It does not matter in what order the main crown or pavilion facets are cut. For example, Huisman patents both disclose a stone which is arrived at by first blocking the pavilion facets at a 41xc2x0 angle and thereafter cutting away additional material, which merely creates star facets, to arrive at steeper angles up to 60xc2x0. In doing so, the opposite result to that achieved by this invention results. That is, unnecessary gem volume is cut away and wasted. More particularly, the Huisman patents require the angling above 41xc2x0 to occur during brillianteering and not during blocking.
The diamond of the instant invention may otherwise be cut as a standard brilliant; or may be provided with a totally different faceting arrangement, so long as the angle and depth of the bottom pavilion facets are made in accordance with the invention.
The technique disclosed herein results in a product which is completely unexpected and dramatically superior to what conventional wisdom in the field would predict.